1. Field of the Invention
The present invention relates to a method of manufacturing a secondary battery, and more particularly, to a method of manufacturing an improved secondary battery adapted to suppress gas exhaust from an electrode assembly sealed within a case of the secondary battery.
2. Description of the Related Art
According to the rapid advancement of small, lightweight and wireless electronic devices such as mobile phones, camcorders, notebook type computers and the like, high-energy density secondary batteries are under vigorous development as power sources for such devices. The secondary batteries are classified into lithium metal batteries using liquid electrolytes, lithium ion batteries and lithium polymer batteries using solid-state polymer electrolytes. The lithium polymer batteries are divided into solid polymer lithium batteries, which do not contain liquid organic electrolytes, and gel polymer lithium batteries, which contain liquid organic electrolytes, according to the kind of electrolyte used.
Lithium batteries use liquid electrolytes or solid electrolytes, solid polymer electrolytes, inter alia. In particular, lithium secondary batteries using polymer electrolytes are free from damage of devices due to leakage of electrolytic solution. Also, since electrolytes of lithium secondary batteries serve as separators, batteries can be made smaller. Also, high-energy density lithium secondary (i.e., rechargeable) batteries can be used as very convenient power sources. Owing to these advantages, much attention is being paid to the lithium secondary batteries as power sources or memory backup sources for portable electronic devices.
FIG. 1 illustrates an example of conventional lithium secondary batteries. Referring to FIG. 1, a secondary battery 10 includes an electrode assembly 11. The electrode assembly 11 includes a positive electrode plate and a negative electrode plate with a separator interposed there between, with the resulting structure being wound. The electrode assembly is in a case 12 which has an insulative case body 12a and a cover case 12b. The electrode assembly 11 is sealed in the case 12. Here, the insulative case body 12a wraps the electrode assembly 11 and has an accommodating portion 12c in which the electrode assembly 11 is seated, and the cover 12b is integrally formed with the insulative case body 12a. Also, the electrode assembly 11 has positive and negative electrode terminals drawn out therefrom.
A method of manufacturing the secondary battery 10 having the above-described configuration includes preparing a positive electrode plate and a negative electrode, preparing the electrode assembly 11 by winding a laminate structure of the positive and negative electrode plates with the separator interposed therebetween, pressing down the electrode assembly 11 to form the laminate structure into a plate-shaped structure, preparing the case 12, which includes the case body 12a and the cover 12b, the case body 12a having the accommodating portion 12c in which the electrode assembly 11 is seated and a gas chamber (not shown) connected to the accommodating portion 12c. The electrode assembly 11 is inserted into the accommodating portion 12c of the case 12, and the resultant structure is sealed therein using the cover 12b. The sealed resultant structure is such that the accommodating portion 12c and the gas chamber are connected to each other. Then, the electrode assembly sealed in the case is thermally fused and initially charged. The gas generated during the initially charging is exhausted into a gas chamber through a connecting path. The connecting path is then sealed and the gas chamber is removed. The secondary battery is then fully charged (so as to reach a saturated charge state).
However, the above-described manufacturing method of a secondary battery involves several problems. Since it is necessary for a separate gas chamber to exhaust and collect the gas generated during the initial charging, a considerable space of a battery case is consumed for installation of the gas chamber. Performing an extra operation for gas exhaustion results in high costs and increased man-hours, making it impossible to increase manufacturability. Also, the gas generated during charging tends to remain in the accommodating portion 12c due to relatively increased resistance when it is leaked to the gas chamber. Thermal fusion performed in such a state may adversely affect the performance and life characteristics of the battery.